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Hemispheric Syndromes
Introduction Hemispheric syndrome is otherwise known as anterior circulation syndrome. It is the result of a large vessel stroke, and occurs when there is proximal occlusion of the int carotid artery, middle and/or anterior cerebral arteries supplying the cerebral hemispheres. The classical clinical picture of a total occlusion is contralateral hemiplegia, hemianesthesia/hyperesthesia, and homonymous hemianopia. Cortical dysfunction is prominent in hemispheric syndrome. Dominant-hemisphere lesions (usually left) can cause receptive aphasia (inferior division of the MCA to the Wernicke area) and/or expressive aphasia (superior division of the MCA to the Broca area). Non-dominant hemisphere lesions can cause amorphosynthesis (defective perception of sensation from one side of the body), hemineglect, and visuospatial deficits. In a MCA stroke, greater involvement is noted in the upper extremities and face (UMN facial palsy) than in the lower extremities (brachiofacial pattern) because the upper extremities of the homunculus are situated more laterally. Conversely, in an ACA stroke, there is greater involvement in the lower extremities and milder upper extremities symptoms. The face is usually spared in an ACA stroke. A large infarction may cause local edema, resulting in brain stem compression and loss of consciousness. The left hemispheric syndrome is thus a stroke syndrome that results from the occlusion of the left ICA, ACA or MCA, and the right hemispheric syndrome results from the occlusion of the right ICA, ACA or MCA. Areas supplied by the MCA, ACA Middle cerebral artery http://www.strokecenter.org/education/ais_vessels/ais049b.html The MCA supplies the lateral (external) part of each cerebral hemisphere. Each MCA proceeds laterally into the lateral sulcus and spreads to supply virtually the entire lateral surface of the cerebral hemisphere, where most of the precentral and postcentral gyri are located. Included in this region is the center for lateral gaze, the motor speech area of Broca, and the sensory language area of Wernicke. The MCA gives rise to lenticulostriate arteries that supply deep structures of the diencephalon and telencephalon, including the putamen, part of the caudate nucleus, the outer globus pallidus, the posterior limb of the internal capsule, and the corona radiata. Anterior cerebral artery http://www.strokecenter.org/education/ais_vessels/ais049a.html The ACA supplies the frontal and medial part of the cerebrum. Each ACA runs medially, superior to the optic nerve, and enters the longitudinal fissure. Then it follows the corpus callosum supplying the anterior four fifths of the corpus callosum and medial aspect of the frontal and parietal lobes. Deep branches, arising near the circle of Willis (proximal or distal to the anterior communicating artery), supply the anterior limb of the internal capsule, the inferior head of the caudate nucleus, and the anterior part of the globus pallidus. Since parts of the precentral and postcentral gyri extend onto the medial surface of the frontal and parietal lobes, ACA occlusions cause contralateral motor and somatosensory deficits, primarily of the lower extremities. Clinical findings Infarction of the various territories that are supplied by the occluded large vessel cause the various signs and symptoms of the hemispheric syndromes. Evaluation Hemispheric syndrome is the result of a large vessel stroke. Large vessel strokes result primarily from cardioembolism or thrombo-embolism from atherosclerostic large blood vessels. In the case of MCA strokes, cardioembolism accounted for approximately 50% of total MCA strokes, 34% of deep MCA strokes, and 41% of cortical strokes in a study by Moulin and coauthors. On the other hand, primary atherosclerosis of the MCA and branches accounts for only 7-8% of symptomatic MCA disease. The latter may however, be higher in Asian patients, because of the higher prevalence on intracranial atherosclerosis. Since embolism is an important cause of hemispheric strokes, careful clinical evaluation should be rigorously performed to elucidate cardiac or carotid artery lesions that could predict future embolic events. Important aspect of examination include palpating the pulse daily (for AF), checking for displacement of apex beat, detection of cardiac murmurs, elucidating signs of of heart failure and auscultating for carotid bruit. Diagnostic studies may include carotid ultrasound, trans-thoracic and esophageal echocardiography studies, and telemetry.